Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Bats save energy by drawing in wings on upstroke

11.04.2012
Whether people are building a flying machine or nature is evolving one, there is pressure to optimize efficiency. A new analysis by biologists, physicists, and engineers at Brown University reveals the subtle but important degree to which that pressure has literally shaped the flapping wings of bats.

The team's observations and calculations show that by flexing their wings inward to their bodies on the upstroke, bats use only 65 percent of the inertial energy they would expend if they kept their wings fully outstretched. Unlike insects, bats have heavy, muscular wings with hand-like bendable joints. The study suggests that they use their flexibility to compensate for that mass.

"Wing mass is important and it's normally not considered in flight," said Attila Bergou, who along with Daniel Riskin is co-lead author of the study that appears April 11 in the Proceedings of the Royal Society B. "Typically you analyze lift, drag, and you don't talk about the energy of moving the wings."

The findings not only help explain why bats and some birds tuck in their wings on the upstroke, but could also help inform human designers of small flapping vehicles. The team's research is funded by the U.S. Air Force Office of Sponsored Research.

"If you have a vehicle that has heavy wings, it would become energetically beneficial to fold the wings on the upstroke," said Sharon Swartz, professor of ecology and evolutionary biology at Brown. She and Kenneth Breuer, professor of engineering, are senior authors on the paper.

The physics of flexed flapping

The team originally set out to study something different: how wing motions vary among bats along a wide continuum of sizes. They published those results in 2010 in the Journal of Experimental Biology, but as they analyzed the data further, they started to consider the intriguing pattern of the inward flex on the upstroke.

That curiosity gave them a new perspective on their 1,000 frames-per-second videos of 27 bats performing five trials each aloft in a flight corridor or wind tunnel. They tracked markers on the bats, who hailed from six species, and measured how frequently the wings flapped, how far up and down they flapped, and the distribution of mass within them as they moved. They measured the mass by cutting the wing of a bat that had died into 32 pieces and weighing them.

The team fed the data in to a calculus-rich model that allowed them to determine what the inertial energy costs of flapping were and what they would have been if the wings were kept outstretched.

Bergou, a physicisist, said he was surprised that the energy savings was so great, especially because the calculations also showed that the bats have to spend a lot of energy — 44 percent of the total inertial cost of flapping — to fold their wings inward and then back outward ahead of the downstroke.

"Retracting your wings has an inertial cost," Bergou said. "It is significant but it is outweighed by the savings on the up and down stroke."

The conventional wisdom has always been that bats drew their wings in on the upstroke to reduce drag in the air, and although the team did not measure that, they acknowledge that aerodynamics plays the bigger role in the overall energy budget of flying. But the newly measured inertial savings of drawing in the wings on the upstroke seems too significant to be an accident.

"It really is an open question whether natural selection is so intense on the design and movement patterns of bats that it reaches details of how bats fold their wings," Swartz said. "This certainly suggests that this is not a random movement pattern and that it is likely that there is an energetic benefit to animals doing this."

David Orenstein | EurekAlert!
Further information:
http://www.brown.edu

More articles from Life Sciences:

nachricht Not of Divided Mind
19.01.2017 | Hertie-Institut für klinische Hirnforschung (HIH)

nachricht CRISPR meets single-cell sequencing in new screening method
19.01.2017 | CeMM Forschungszentrum für Molekulare Medizin der Österreichischen Akademie der Wissenschaften

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

New Study Will Help Find the Best Locations for Thermal Power Stations in Iceland

19.01.2017 | Earth Sciences

Not of Divided Mind

19.01.2017 | Life Sciences

Molecule flash mob

19.01.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>